As a filing tool for binding documents punched by a multi-hole punching device or commercially available loose leaf sheets, there has been conventionally and widely used a filing binder in which metal or resin foldable ring binder is fixed to an inside of a spine surface of a file cover with a front surface, the spine surface and a rear surface.
Further, there are various shapes of single-body ring binders with no file covers. Among the single-body ring binders, there is a ring binder having comb-like resin strips in a planar shape which are bent cylindrically so that comb teeth are ring-shaped (for example, JP-A-2001-018571). If the cylindrical ring binder is expanded, a large number of comb teeth are inserted into punched holes of a sheet(s), respectively and thereafter expansion is cancelled, so that the ring binder is restored to the cylindrical shape, thereby binding the sheets.
Further, as ring binders permitting easier mounting, there is a resin ring binder in which ½ ring portions are arranged on both sides of a slender spine portion, and the ½ ring portions constituting pairs across the spine portion are closed in a ring shape so that their tips are fit to each other, thereby binding the sheets (JP-A-2000-289376), and a resin ring binder in which the ring portion is divided into three parts (e.g. JP-A-2003-320779).
The resin ring binder with no the file cover is light in weight and large in the sheet spreading angle so that it is a simple and convenient filing tool. However, since it is not accompanied by the spine surface, when the booklets bound with the ring binder are arranged or stacked on a bookshelf, the filing name of each booklet is difficult to know, and the entire booklet is likely to warp. For the reason, in order to bind the document with high importance or frequent use, the binder equipped with the file cover is employed. However, if a cover is required for the booklet once bound with the ring binder, work of removing the booklet from the ring binder and transferring it into the binder equipped with the cover must be executed. The work requires time and labor.